1. Field of the Invention
This invention relates to an ice making machine and more particularly to an ice making machine wherein feed water is supplied only during the ice making cycle to the deicing or harvesting water tank for improving temperature characteristics of the harvesting water.
2. Description of the Prior Art
There have been adopted and proposed various constructions of this kind of the ice making machines. Typical of these is an ice making machine shown and described in Japanese Utility Model Publication No. 38692/1984.
In the ice making machine of Publication No. 38692/1984, when the harvesting water should be decreased from a predetermined water level which is the full water level, it is sensed by a foot switch which then issues an output signal for opening a magnetic valve connected to an external water source or water main for supplying water from the water main into the harvesting water tank. When the water is supplied in this manner, the temperature of the harvesting water is lowered. Thus, when the harvesting water is sprayed onto the freezing plates, it takes a lot of time before the harvesting of ice products from the freezing plates is terminated, so that the operational efficiency of the ice making machine is lowered.
In order to combat this, it is a conventional practice to design the harvesting water tank to be extremely large to prevent rapid falls in the temperature of the harvesting water due to introduction of the low temperature feed water. However, this turns out to be a barrier to reducing the size of the ice making machine.
Conversely, when the harvesting water tank is designed to be extremely small, the harvesting water temperature is significantly lowered in winter so that a large size heat exchanger is required in order to keep the harvesting water temperature at a predetermined value. On the other hand, the water temperature in the harvesting water tank is unusually increased during summer with resulting increase in the costs involved in surface treatment of the heat exchanger provided in the harvesting tank and heat resisting treatment of the harvesting water tank itself. In addition, harvesting water of an unusually high temperature is supplied to the freezing plates during harvesting so that the yield of the ice products is lowered due to excess ice melting. Since the harvesting water is used as the ice making water in the next ice making cycle, the ice making water at the next ice making cycle is at an elevated temperature, resulting in a decreased yield in ice products. Such reduction in the ice making capacity represents an increase in the load on the freezing device thus leading to shortened service life of the freezing device.